The invention relates to a picture display device comprising a closed envelope having substantially parallel front and rear walls, a layer of luminescent material on the inner surface of the front wall, electron-emissive means for generating at least one electron beam and a selection electrode system for causing the or each electron beam to be substantially perpendicularly incident on the layer of luminescent material so that the or each beam scans at least a part of the layer of luminescent material for building up a picture, and a fine-deflection structure comprising individual electron beam channels with each of which a first and a second deflector electrode is associated, which deflector electrodes can be energized to deflect an electron beam from the electron beam channel and which can be suitably controlled so that the electron beam can be accurately directed onto a desired surface element of the layer of luminescent material.
As compared with the conventional cathode ray tube a construction of the type described above has considerable advantages because shallow, flat television display devices can be realized by means of this construction. Points of consideration are, among others, obtaining a uniform brightness and resolving power throughout the picture surface independently of the driven pixel and the possibility of colour selection in colour display devices or the possibility of correcting the electron beams in high-resolution monochrome display devices.
A device of the type described in the opening paragraph is known, for example from the published British Patent Application No. 2,124,017. This Application relates to a device in which the luminescent screen is scanned by means of one electron beam which is produced by one cathode. Other shallow, flat display devices operate with, for example line cathodes producing a ribbon of electrons or with a large number of aligned cathodes producing a plurality of parallel electron beams.
The display tubes for shallow, flat display devices hitherto proposed often use a very fine electrode structure to obtain a limited horizontal (post)-deflection of electron beams (for example for creating colour, and/or for correcting certain types of alignment errors). The said fine-deflection structure comprises strip-shaped electrodes on either side of each beam so that a limited deflection of the beam is obtained by way of potential differences.
In addition to the use of metallized glass or ceramic material structures, research is particularly being done in the field of metal deflector electrode structures.
The following requirements are imposed on these fine-deflection electrode pairs: the electrodes must be mutually insulated, the electrode pairs must be electrically coupled so that the pairs can be switched simultaneously, the electrode structure must have a high accuracy to ensure uniform scanning and to provide the possibility of combination with the phosphor pattern on the screen and with mask structures in the interior.
In the known embodiments, research has been done in long electrodes which extend throughout the height of the display window and are thus strip-shaped. Problems in this field are:
handling, positioning, securing and keeping the strips in one plane,
the sensitivity to vibrations of a strip structure,
the mutual insulation of the strips and the combined coupling of the pairs,
designing the strips while taking the etching geometry, plate thickness, and the formation of burrs into account,
separating the strips if a temporary connection between the strips for the purpose of improved handling is allowed.